A method for capacity design and parameter optimization of CLCC auxiliary branch aiming at grid application requirements

Abstract

The application discloses a kind of CLCC auxiliary branch capacity design and parameter optimization method with power grid application demand as target, first based on the operating characteristics of direct current transmission system, the capacity matching model of main auxiliary branch is established, and the overall loss of converter valve is reduced by optimizing the switching time of main auxiliary branch of converter valve, improve the reliability of commutation process.Subsequently, introduce loss calculation and economy evaluation model, the overall benefit of CLCC is quantitatively analyzed, and combined with electromagnetic simulation, system verification is carried out, to ensure that the optimized converter valve can effectively prevent commutation failure under various fault conditions.The application analyzes the different functions of main branch and auxiliary branch and their influence on commutation process, and proposes an optimization design scheme based on system demand orientation to improve the economy and engineering applicability of CLCC converter valve.

Description

Technical Field

[0001] This invention relates to the field of high voltage direct current (HVDC) transmission technology, and in particular to a method for designing and optimizing the capacity and parameters of CLCC auxiliary branches based on the needs of power grid applications. The aim is to improve the adaptability of CLCC converter valves in multi-feed DC transmission systems, optimize the capacity configuration of their main and auxiliary branches, and reduce the risk of commutation failure, thereby enhancing the safety and stability of DC transmission systems. Background Technology

[0002] With the development of the global energy internet and the large-scale integration of clean energy, the advantages of high-voltage direct current (HVDC) transmission technology in long-distance, large-capacity power transmission are becoming increasingly prominent. However, traditional thyristor-based commutation converters (LCC-HVDC) are highly dependent on the AC system to provide commutation voltage during operation. When the AC system fails, the converter may be unable to complete commutation, resulting in commutation failure and affecting the stable operation of the system.

[0003] In recent years, Controlled Commutation Converter Valve (CLCC) technology has been proposed. Based on the LCC converter, this technology introduces an auxiliary branch and utilizes the active turn-off capability of Insulated Gate Bipolar Transistors (IGBTs) for commutation control, fundamentally reducing the risk of commutation failure. However, existing CLCC design methods lack systematic research on capacity optimization for both main and auxiliary branches. Current engineering designs generally allocate capacity based on rated current capability, failing to fully consider grid operation requirements, commutation characteristics, and converter valve loss optimization.

[0004] Therefore, this invention proposes a CLCC auxiliary branch capacity design and parameter optimization method aimed at the needs of power grid applications. The aim is to combine power grid operation requirements, optimize the capacity configuration of main and auxiliary branches, reduce commutation losses, and improve the economy of converter valves. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing CLCC converter valve capacity design methods by proposing a main and auxiliary branch capacity optimization method based on power grid application requirements. By calculating key indicators such as inverter-side arc extinction angle and short-circuit ratio, the capacity matching of the main and auxiliary branches is optimized, and a CLCC loss calculation and economic analysis model is established to improve the reliability and engineering adaptability of the converter valve.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for designing and optimizing the capacity and parameters of CLCC auxiliary branches based on power grid application requirements, the method comprising the following steps:

[0008] S1: Establish a capacity matching model for main and auxiliary branches, and calculate the basic parameters of main and auxiliary branches;

[0009] S2: Optimize the switching time between the main and auxiliary branches based on the aforementioned basic parameters;

[0010] S3: Based on the aforementioned basic parameters, establish a loss model for the controllable commutator valve and optimize the conduction time of the main and auxiliary branches;

[0011] S4: Based on the loss model, establish an economic evaluation model for the controllable commutation valve, evaluate the economic efficiency of the optimized scheme, and verify the feasibility of the optimization strategy through simulation.

[0012] Preferably, the basic parameters include: the number of thyristors and insulated gate bipolar transistors connected in series, their parallel configuration, and their current carrying capacity.

[0013] Preferably, the number N of thyristors connected in series in the main branch is... Th Calculated by the following formula:

[0014]

[0015] Among them, U AM K is the maximum operating voltage of the converter valve bridge arm. CU K is the overvoltage impulse coefficient. b K is the voltage rise factor of the power grid; AU For voltage design margin; K U U is the equalization pressure coefficient; RM This is the rated repetitive peak voltage of the thyristor.

[0016] Preferably, the number N of series-connected insulated gate bipolar transistors in the auxiliary branch is... IGBT Calculated by the following formula:

[0017]

[0018] Among them, U submodule Voltage for each submodule; V device This is the rated voltage of a single insulated-gate bipolar transistor device.

[0019] Preferably, the optimization of the main and auxiliary branch switching time adopts an adjustment method based on the dynamic commutation process, specifically including:

[0020] Set the turn-off time t of the main branch insulated-gate bipolar transistor. off On-time t of the auxiliary branch insulated gate bipolar transistor on Adjust the current transfer time during the commutation phase to ensure that the main branch thyristors can quickly restore their blocking capability after commutation.

[0021] Preferably, the loss model of the controllable commutator valve in S3 includes:

[0022] The conduction loss P of an insulated gate bipolar transistor cond The calculation formula is as follows:

[0023]

[0024] Where V CE I is the saturation voltage of an insulated-gate bipolar transistor. C R is the collector current of an insulated-gate bipolar transistor. CE This is the on-state resistance of an insulated-gate bipolar transistor.

[0025] Preferably, the loss mathematical model of the controllable commutator valve in S3 further includes:

[0026] The on-state loss P of the thyristor Tcond The calculation formula is as follows:

[0027]

[0028] Where V T I is the on-state voltage of the thyristor. TAV I is the average value of the thyristor current. TRMS r is the effective value of the thyristor current. T The on-state slope resistance of the thyristor.

[0029] Preferably, the economic evaluation model for the controllable commutator valve in S4 includes:

[0030] Calculate the total loss cost C of the controllable commutator valve. loss :

[0031]

[0032] Among them, C elec Cost per unit of electricity.

[0033] Preferably, the economic evaluation model for the controllable commutator valve in S4 further includes:

[0034] Calculate the maintenance cost C of the controllable commutator valve. maint And optimize to minimize the total cost C. total :

[0035]

[0036] Preferably, the simulation verification of the feasibility of the optimization scheme specifically includes:

[0037] An electromagnetic transient simulation model of the controllable commutator valve was established in PSCAD / EMTDC software.

[0038] Simulate commutation failure under different fault conditions and verify the effect of optimized design on improving commutation stability.

[0039] The main innovative points of this invention include:

[0040] (1) A method for CLCC capacity configuration and parameter optimization based on grid demand is proposed, which can accurately match the ratio of main and auxiliary branches of CLCC. Specifically, based on the operating characteristics of DC transmission systems, this invention establishes a capacity matching model for main and auxiliary branches, which includes: calculating key indicators such as commutation voltage, short-circuit ratio, and system commutation margin to determine the optimal number and configuration of thyristors in the main branch and IGBTs in the auxiliary branch. Among them, the commutation voltage includes the inverter-side AC bus voltage, DC-side voltage, and the maximum operating voltage (U0) of the converter valve arm. AM Key electrical parameters such as voltage design margin (K) directly affect the stability of the commutation process. The system commutation margin is determined by the voltage design margin factor (K). AU Safety factors such as [missing information] are quantified to ensure the safety margin of the converter valve under abnormal power grid conditions. By analyzing the performance of the CLCC converter valve under different operating conditions, the proportional relationship between the main branch and the auxiliary branch is accurately determined to ensure that the two can work together and reduce the risk of commutation failure.

[0041] (2) The dynamic control strategy of the commutation process is optimized, improving the controllability of the commutation process. Specifically, this invention optimizes the switching time of the main and auxiliary branches, especially adjusting the reverse recovery time of the thyristor in the main branch and the turn-on / turn-off sequence of the IGBT in the auxiliary branch, so as to reduce the overall loss of the converter valve and improve the stability of the commutation process. In addition, this invention introduces an adjustment method based on the dynamic process of commutation. By finely controlling the current transfer time in the commutation stage, the controllability of the commutation process is enhanced, thereby improving the reliability of the entire system.

[0042] (3) This invention provides an analytical basis for the economics of CLCC converter valves and offers technical support for engineering applications. Specifically, this invention constructs a detailed calculation model for converter valve losses, considering factors such as IGBT switching losses and thyristor conduction losses, and conducts a comprehensive economic evaluation in conjunction with equipment costs, power losses, and maintenance costs. Furthermore, this invention quantifies the overall benefits of CLCC converter valves using scientific methods and verifies the optimization scheme through simulation, ensuring that it is not only technically feasible but also economically advantageous. In addition, it proposes an optimization strategy to minimize total costs, providing solid technical support for engineering applications.

[0043] This method can significantly reduce the risk of commutation failure in high-voltage direct current transmission systems and improve the stability and security of the power grid. Attached Figure Description

[0044] Figure 1 This is a flowchart of a parameter matching method for CLCC in one embodiment of the present invention;

[0045] Figure 2 This is a structural diagram of the inverter-side system in one embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of the working principle of the CLCC converter valve in one embodiment of the present invention;

[0047] Figure 4 This is a diagram showing the internal topology of a CLCC valve in one embodiment of the present invention;

[0048] Figure 5 This is a loss distribution diagram of a CLCC valve device in one embodiment of the present invention;

[0049] Figure 6 This is a complete inverter circuit structure in a single valve in one embodiment of the present invention;

[0050] Figure 7 This is a flowchart illustrating the parameter value optimization process in one embodiment of the present invention;

[0051] Figure 8 This is a flowchart of parameter determination in one embodiment of the present invention;

[0052] Figure 9 This is a CLCC simulation model of PSCAD in one embodiment of the present invention;

[0053] Figure 10 The waveform data obtained after simulation in one embodiment of the present invention represents the power emitted by each bridge arm in the main and auxiliary bridge arm branches. Detailed Implementation

[0054] The following will refer to the appendix. Figures 1 to 10 Specific embodiments of the invention are described in detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0055] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0056] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0057] This invention provides a method for designing the capacity and optimizing the parameters of CLCC auxiliary branches based on the needs of power grid applications, such as... Figure 1 As shown, the method includes:

[0058] Step 1: Establish a capacity matching model for the main and auxiliary branches. By analyzing the current distribution characteristics during the commutation process, reasonably determine the number of series / parallel connections of the thyristors in the main branch and the insulated gate bipolar transistors (IGBTs) in the auxiliary branch to achieve optimal capacity matching.

[0059] Step 2: Optimize the commutation timing of the main and auxiliary branches, adjust the reverse recovery time of the thyristor in the main branch and the turn-on / turn-off timing of the IGBT in the auxiliary branch, so as to reduce the loss of the converter valve and improve the controllability of the commutation process.

[0060] Step 3: Construct a converter valve loss calculation and economic analysis model. Based on IGBT switching losses, thyristor on-state losses, conduction voltage, and energy losses during commutation, establish a complete converter valve loss calculation method and optimize its operating costs.

[0061] Step 4: Verify the effectiveness of the optimization scheme through PSCAD / EMTDC simulation.

[0062] In one embodiment, the present invention provides a method for designing and optimizing the capacity and parameters of CLCC auxiliary branches based on power grid application requirements, including:

[0063] The system was modeled using PSCAD / EMTDC electromagnetic transient simulation software. The complete inverter circuit structure in a single valve is shown below. Figure 6 As shown in the figure, the converter valve consists of six bridge arms, and the internal topology of each bridge arm is as follows: Figure 4As shown. The inverter-side system structure is as follows. Figure 2 As shown. During normal operation of the CLCC valve, the external triggering sequence is compatible with the grid-connected phase converter (LCC), allowing the main branch to initiate commutation at a natural 120° commutation angle. After the commutation process begins, the main branch current is lower than the preset current threshold I. v Afterwards, the main branch is closed, and the IGBTs and thyristors of the auxiliary branch are turned on, transferring the load current to the auxiliary branch. Once the natural commutation process is complete and the auxiliary branch current drops to zero, the auxiliary branch IGBTs should be turned off, and the commutator arm should bear the positive voltage. The working principle is as follows: Figure 3 As shown.

[0064] Calculate the capacity that the receiving end should provide based on the sending end's requirements and configure it appropriately:

[0065] 1) Considering inverter efficiency

[0066] System efficiency ( (): This includes inverter efficiency and transmission efficiency.

[0067] Inverters experience energy losses during the conversion of direct current (DC) to alternating current (AC), and their efficiency is typically between 90% and 96%. Therefore, the capacity of the receiving-end inverter should be greater than the required sending-end capacity divided by the inverter's efficiency.

[0068] 2) Consider the transmission requirements of the sending end.

[0069] Required capacity at the sending end ( ): Determine the required active and reactive power at the sending end based on engineering practice needs. 3) Consider transmission losses.

[0070] Transmission loss ( Based on the transmission distance I, line impedance R, etc., estimate the power loss during transmission:

[0071]

[0072] To ensure the inverter can still operate normally under extreme conditions, a safety factor Ks needs to be introduced, typically between 1.2 and 1.5. That is, the receiving-end inverter capacity = (sending-end required capacity ÷ inverter efficiency) × safety factor.

[0073]

[0074] Among them, S r K represents the capacity of the receiving-end inverter. s This is for the safety factor.

[0075] 4) Consider the power factor of the sending-end load.

[0076] Sending end load power factor ( Determine the power factor requirement at the sending end, which affects the inverter's reactive power supply capability.

[0077] In practical applications, the load's power factor affects the calculation of the inverter's output power. The power factor is the cosine of the phase difference between the load current and voltage, representing the load's efficiency in utilizing current. Knowing the power required at the sending end and the power factor allows for a more accurate calculation of the power required by the receiving-end inverter. The calculation formula is as follows:

[0078]

[0079] 5) The active power P that the receiving-end inverter should output r

[0080]

[0081] 6) Inverter capacity design at the receiving end

[0082] The capacity of the receiving-end inverter depends not only on active power but also on reactive power demand. The capacity (apparent power) of the receiving-end inverter can be determined by the following formula:

[0083]

[0084] Among them, reactive power Q r It should be calculated based on the power factor of the sending-end load:

[0085]

[0086] The capacity S of inverters in parallel 总 :

[0087]

[0088] 7) Consider some additional margin

[0089] In practical design, the system's operational margin and backup capacity need to be considered, including the following two aspects:

[0090] Overload capacity: When designing inverters, a margin of 1.1 times or more is usually considered.

[0091] Faults and dynamic response: In power systems, load fluctuations can lead to changes in instantaneous power demand, and the inverter capacity should be able to cope with these dynamic changes.

[0092] Formula for calculating the inverter-side arc extinction angle γ:

[0093]

[0094] In the formula, k is the transformer turns ratio on the inverter side; I d X is direct current; rU is the equivalent commutation reactance on the inverter side; L β is the AC bus line voltage (RMS) on the inverter side; β is the leading firing angle.

[0095] Example as follows: Assume a transformer in a system has a turns ratio k=1.0, I d =5000A, X r =0.1Ω, U L =565.7KV, β=20°. Therefore:

[0096]

[0097] Compare the inverter-side arc extinction angle γ with the safety threshold: if γ ≥ the safety threshold, reduce auxiliary branch redundancy; if γ < the safety threshold, increase the number of GBTs or the conduction time, such as... Figure 7 As shown.

[0098] The calculation method for Short-Circuit Ratio (SCR):

[0099]

[0100] In the formula, S AC The short-circuit capacity (MVA) of the converter station's AC system; P DC The rated DC transmission power (MW) of the converter station;

[0101] Example as follows: Suppose S in a system AC =9000MVA, P DC =3000MW. Then SCR=3.0. The larger the SCR, the stronger the AC support capability of the system and the less likely it is to fail.

[0102] Main and auxiliary branch capacity configuration:

[0103] By calculating the power capacity of the converter valve on the inverter side of the receiving end, the number of components connected in series in the main and auxiliary branches of the converter valve can be obtained. Based on the number of components, the switching time of the main and auxiliary branches can be calculated more reasonably, and the optimal auxiliary branch conduction time that can prevent system commutation failure can be calculated under different demand conditions.

[0104] Example as follows:

[0105] Suppose we have the following engineering parameters:

[0106]

[0107] Calculation of receiving-end inverter capacity:

[0108] Component quantity configuration for main and auxiliary branches:

[0109] The number of thyristors in the main branch circuit is:

[0110] Right now

[0111] Parameter description: KCU=1.5 is the overvoltage impulse coefficient; Kb=1.1 is the grid voltage rise coefficient; KAU=1.2 is the voltage design margin; KU=0.85 is the voltage equalization coefficient.

[0112] The number of auxiliary branch IGBTs is as follows: designed according to submodules (file) Figure 4 ):

[0113] Submodule voltage Usubmodule=2 kV

[0114] Redundancy coefficient Kredundancy = 1.4 (due to the relatively weak SCR of 2.1)

[0115]

[0116] Design adjustments: Considering dynamic voltage surges, the final design uses two IGBTs connected in series / submodule.

[0117] (1) The basic timing settings are as follows:

[0118]

[0119] (2) Dynamic adjustment strategy (based on γ and SCR)

[0120] like Figure 8 As shown, if γ < 8°, then increase t. on Up to 85 μs, otherwise maintain t on =70μs. If SCR < 2.5, increase K. redundancy Up to 1.5. If SCR ≥ 2.5, then K redundancy Unchanged. The CLCC converter valve consists of multiple sub-modules, such as... Figure 2 As shown, each submodule typically contains one main branch and one auxiliary branch, and each submodule contains one or more IGBTs and diodes. The power capacity of each submodule can be calculated using the following formula:

[0121]

[0122] in:

[0123]

[0124] P submodule This is the power capacity of each submodule; V submodule It is the voltage of each submodule; I submodule The current of each submodule, Pr It is the active power that the receiving-end inverter should output.

[0125] Each submodule typically contains one main branch and one auxiliary branch. The number of components connected in series in the main and auxiliary branches can be calculated using the following formula:

[0126]

[0127] N devices It is the number of components connected in series in each submodule; V device This is the rated voltage of each component.

[0128] Considering economic factors, only 1-2 IGBTs are typically used in the main branch of a CLCC converter valve to handle the turn-off function of the bridge arm. Therefore, this invention mainly needs to consider the capacity and number of thyristors. The number of thyristors, N. Th The calculation method is as follows:

[0129]

[0130] K CU This is the overvoltage impulse factor, ranging from 1.3 to 1.6, depending on the completeness of the overvoltage protection measures in the equipment. AM It refers to the operating peak voltage of the arm, specifically the forward peak voltage U. ATM Or the reverse peak voltage U of the arm ARM When calculating, take the larger of the two. K b K is the voltage rise factor of the power grid, which is generally taken as 1.05 to 1.1, and can be taken as a higher value in special cases. AU This is the voltage design margin, typically 1 to 2, depending on the reliability of the components and the reliability requirements of the equipment. K U This is the equalization pressure coefficient, typically taken as 0.8 to 0.9. RM It is the rated repetitive peak voltage of the series device.

[0131] Optimize the switching time between main and auxiliary branches: Set the main IGBT turn-off time t through the gate drive circuit. off (Control shutdown command timing) and auxiliary IGBT turn-on time t on (Control the turn-on command timing), adjust the current transfer time to near the main IGBT fall time, and add a dead time. This ensures smooth current transfer, and the main IGBT has sufficient carrier clearance time in the zero-current state, thus quickly restoring blocking capability after commutation.

[0132] Specifically, such as Figure 3 As shown, when the current is flowing normally, the main branch IGBT is turned on and the auxiliary branch IGBT is turned off, so that the current flows normally through the main branch thyristor and the main branch IGBT.

[0133] When natural commutation is required, the main branch IGBT is turned off, and the auxiliary branch IGBT is turned on, so that the current is transferred from the main branch to the auxiliary branch, and the auxiliary branch thyristor and auxiliary branch IGBT continue to carry the current.

[0134] During the auxiliary branch freewheeling process, the current status is monitored. When the current drops to 0, the auxiliary branch IGBT is turned off to complete the natural commutation process.

[0135] This method achieves smooth current transfer during commutation, ensuring the stability and reliability of the system.

[0136] Loss analysis of controllable commutator valves:

[0137] In CLCC converter valves, most of the losses that need to be calculated are borne by their main components. Specific losses are as follows: Figure 5 As shown, the losses of the CLCC converter valve include: IGBT losses, thyristor losses, and other losses (neglected).

[0138] IGBT losses include:

[0139] Static losses include on-state losses and off-state losses (which are ignored). On-state losses refer to the power losses generated by the IGBT in the on-state.

[0140] Switching losses include necessary switching losses and additional switching losses. Necessary switching losses are unavoidable losses during the normal switching process of IGBTs; additional switching losses are extra losses caused by additional factors (the value of additional switching losses is too small to be ignored).

[0141] Thyristor losses include:

[0142] Static losses: include on-state losses and off-state losses (ignored). Similar to IGBTs, on-state losses refer to the power loss of a thyristor in the on-state.

[0143] Switching losses include necessary switching losses and additional switching losses. Necessary switching losses are unavoidable losses during normal switching of the thyristor; additional switching losses are losses caused by external factors (the value of additional switching losses is too small to be considered). Among these, the conduction losses of the IGBT... and the on-state loss P of the thyristor Tcond The calculation method is as follows:

[0144]

[0145] Among them I C R is the collector current of the IGBT. CEV is the on-state resistance between the collector and emitter. CE It is the saturation voltage of the IGBT; I TAV It is the average value of the thyristor current, I. TRMS It is the effective value of the thyristor current, V T It is the average on-state voltage of the thyristor, r T It is the on-state slope resistance of the thyristor.

[0146] IGBT switching losses are divided into necessary switching losses and additional switching losses, where the necessary switching loss P SW-T The calculation method is as follows:

[0147]

[0148] f SW It is the switching frequency of the IGBT, E on It is the turn-on loss, E off It is the shutdown loss.

[0149] Among them, the turn-on loss E on Turn-on loss E refers to the energy loss generated by an IGBT during the transition from the off state to the on state. on It can be calculated using the following formula:

[0150]

[0151] Where t on(10%) and t on(90%) This refers to the time required for the IGBT collector current to rise to 10% and 90% of its normal value, respectively. V CE (t) is the saturation voltage of the IGBT, I C (t) is the collector current.

[0152] Similarly, the turn-off loss E off The calculation method is as follows:

[0153]

[0154] Where t off (10%) and t off (90%) is the time required for the IGBT collector current to drop to 10% and 90% of its normal value. V CE (t) is the voltage between the collector and the emitter, I C (t) is the collector current.

[0155] Necessary switching losses of thyristors Mainly composed of turn-on loss (P TT ) and turn-off loss (P RQ It consists of two parts, and its calculation formula is:

[0156]

[0157] Where P TT and P RQ The calculation method is as follows:

[0158]

[0159]

[0160] Where T is the modulation period, P TT t in on (10%) and t on (90%) represents the time it takes for the thyristor current to rise to 10% and 90% of its normal value, t off (10%) and t off (90%) represents the time it takes for the thyristor current to drop to 10% and 90% of its normal value, V T It is the average on-state voltage of the thyristor, I. T This refers to the current flowing through the thyristor within the open-circuit zone. The economic evaluation model for controllable commutator valves includes:

[0161] Calculate the total loss cost C of the controllable commutator valve. loss :

[0162]

[0163] Among them, C elec Cost per unit of electricity.

[0164] Calculate the maintenance cost C of the controllable commutator valve. maint And optimize to minimize the total cost C. total :

[0165]

[0166] In another embodiment, the calculation process is exemplified as follows:

[0167]

[0168] The total loss cost is:

[0169]

[0170] Maintenance costs ,in Equipment cost (100,000 RMB / unit for thyristors, 150,000 RMB / unit for IGBTs); Km: Maintenance fee rate (4%).

[0171] The final optimization result of the case is:

[0172]

[0173] In another embodiment, assume that the design requirements of a certain CLCC converter valve are as follows: the maximum operating voltage U of the converter valve bridge arm. AM =800kV; Overvoltage impulse coefficient K CU =1.5; Grid voltage rise coefficient K b =1.1; Voltage design margin K AU =1.2; Equal pressure coefficient K U =0.85; Rated repetitive peak voltage U of thyristor RM =8.5kV; Submodule voltage U submodule =2kV; Rated voltage of a single IGBT V device =3.3kV.

[0174] Based on the number N of thyristors connected in series in the main branch circuit Th formula:

[0175]

[0176] Substituting the parameters, we get:

[0177] Based on the number of IGBTs connected in series in the auxiliary branch formula:

[0178]

[0179] Assuming redundancy coefficient K redundancy Substituting 1.2 into the parameters, we get:

[0180] After determining the number of thyristors and IGBTs connected in series, parallel configuration is primarily to meet current carrying capacity requirements. This means that if a single path cannot handle the required current, parallel paths need to be added to distribute the current load. Specifically:

[0181]

[0182] The appropriate number of thyristors connected in parallel can be selected based on the required current carrying capacity and the rated current of a single thyristor. If a single thyristor cannot carry the expected current, multiple thyristors need to be connected in parallel to increase the total current carrying capacity.

[0183] Similarly, IGBTs can be configured to increase current carrying capacity by connecting more IGBTs in parallel, depending on actual needs.

[0184] Result Correction: After rounding and adding redundancy, the final number of thyristors connected in series in the main branch was determined to be 242. This was rounded down to 1 IGBT, but considering dynamic voltage fluctuations, 2 IGBTs were ultimately used in series.

[0185] Assuming a certain operating condition: IGBT saturation voltage V CE =2.1 V; collector current I C =1500 A; On-state resistance R CE =0.001 Ω. Based on the IGBT's on-state loss P... cond formula:

[0186]

[0187] Substitute parameters for calculation:

[0188]

[0189] PSCAD model parameter settings: Build a CLCC converter valve model, such as Figure 9 As shown, 242 thyristors are set in the main branch and 2 IGBTs in the auxiliary branch. The simulated AC bus voltage drops to 0.7 pu for 100 ms.

[0190] Figure 10 The waveform data obtained after simulating the CLCC model built using PSCAD simulation software is shown. This data represents the power emitted by each arm in the main and auxiliary arm branches. P1_1 is the power waveform diagram of the main branch in the CLCC, and P1_2 is the power waveform diagram of the auxiliary branch in the CLCC.

[0191] The simulation results are compared below:

[0192] Before optimization: the number of commutation failures was 5 per failure; the total loss was 12.8MW.

[0193] After optimization: the number of commutation failures was reduced to 1 per failure; the total loss was 9.2MW.

[0194] Cost savings: (12.8-9.2)×0.1 yuan / kWh×8760 h=315,000 yuan / year.

[0195] The economic efficiency was verified by analyzing the total losses before and after optimization. After optimization using this invention, the maintenance cost was reduced by 20%, which verifies the economic efficiency of the optimization scheme.

[0196] The foregoing general description of the invention and its specific embodiments should not be construed as a limitation on the technical solution of the invention. Those skilled in the art, based on the disclosure of this application, can add, reduce, or combine the disclosed technical features in the foregoing general description and / or specific embodiments (including examples) without departing from the constituent elements of the invention, to form other technical solutions within the scope of protection of this application.

Claims

1. A CLCC auxiliary branch capacity design and parameter optimization method targeting grid application requirements, characterized in that, The method comprises the following steps: S1: establishing a main and auxiliary branch capacity matching model, and calculating basic parameters of the main branch and the auxiliary branch; S2: optimizing the main and auxiliary branch switching time based on the basic parameters; S3: establishing a controllable commutation converter loss model based on the basic parameters; wherein the controllable commutation converter loss model comprises: On-state loss P of an insulated gate bipolar transistor cond The calculation formula is as follows: ， where V CE is the saturation voltage of the insulated gate bipolar transistor, I C is the collector current of the insulated gate bipolar transistor, R CE is the on-state resistance of the insulated gate bipolar transistor; The on-state loss P of the thyristor Tcond The calculation formula is as follows: ， where V T is the on-state voltage of the thyristor, I TAV is the average value of the thyristor current, I TRMS is the effective value of the thyristor current, r T is the on-state slope resistance of the thyristor; S4: establishing a controllable commutation converter economy evaluation model based on the loss model, evaluating the economy of the optimized scheme, and verifying the feasibility of the optimization strategy through simulation; wherein The controllable commutation converter economy evaluation model comprises: Calculating the total loss cost C of a controllable phase commutated converter valve loss : ， where C elec is the unit cost of electrical energy; Calculating maintenance costs C of a controllable phase-changing converter valve maint and optimizing to minimize the total costs C total : 。 2. The method of claim 1, wherein, The basic parameters comprise the series number, parallel configuration and current-carrying capacity of thyristors and insulated gate bipolar transistors.

3. The method of claim 2, wherein, The number of series N of main branch thyristors Th is calculated from the following equation: ， wherein, U AM is the maximum operating voltage of the converter valve bridge arm; K CU is the overvoltage surge factor; K b is the grid voltage rise factor; K AU is the voltage design margin; K U is the voltage equalization factor; U RM is the rated repetitive peak voltage of the thyristor.

4. The method of claim 2, wherein, The number of series N of auxiliary branch insulated gate bipolar transistors IGBT Is calculated from the following formula: ， where U submodule is the voltage of each sub-module; V device is the rated voltage of a single insulated gate bipolar transistor device.

5. The method of claim 1, wherein, The optimization of the main and auxiliary branch switching time adopts an adjustment method based on commutation dynamic process, and specifically comprises: Setting the turn-off time t of the main leg insulated gate bipolar transistor off and the turn-on time t of the auxiliary leg insulated gate bipolar transistor on The current transfer time of the commutation phase is adjusted to ensure that the main leg thyristor recovers blocking capability quickly after commutation.

6. The method of claim 1, wherein, The verification of the feasibility of the optimization scheme through simulation specifically comprises: Establishing an electromagnetic transient simulation model of the controllable commutation converter in software; Simulating commutation failure conditions under different fault conditions, and verifying the improvement effect of the optimization design on commutation stability.

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